(1)The data of MOSI line is sampled on the rising
edge of SCK;
(2)The data of MISO line changes on the falling
edge of SCK;
(3) SCK can be high level, also low level when it
is free status;
(4)During the serial communication, left-hand
digit of data must be read out firstly.
SPI interface junction circuit just shows in Fig.5: